多无人机三维群集算法的适用性研究与改进

针对多无人机群三维空间运动的复杂群集控制问题,提出了基于生物群集行为、依据Reynolds规则描述的三维群集控制算法。已有的研究大多将无人机群集运动简化为二维平面运动,但这不符合实际控制需求。为此,将群集控制算法和人工势场算法推广到三维无人机群集控制中,建立了三维无人机群空间运动模型,通过多种不同条件下的仿真,研究了两种算法在三维群集控制中的有效性。结果显示两种算法用于三维群集控制均具有一定效果,但相对二维所需要的条件更为苛刻。同时,注意到智能算法具有更好的群体聚集效果,而人工势场算法则避碰效果更迅速明显。据此,对人工势场算法和智能算法进行了改进,通过在距离大于平衡点时采用智能算法聚集,在距离小于平衡点时采用人工势场算法避碰,得到能同时获得更好的聚集、避碰效果的新的群集控制算法。     

Accuracy of long-term forecasting geosynchronous satellite motion

The accuracy of forecasting geosynchronous satellite motion for 242-year term of forecast using a numerical model of artificial satellite motion taking into account the main perturbing factors including nonsphericity of the Earth’s gravitational field, attraction by the Moon and the Sun, tides inside the Earth, direct light pressure with allowance for the Earth’s shadow effect, and the Pointing–Robertson effect is considered. It is demonstrated that in this case, perturbations of the Earth’s gravitational field harmonics up to the 27th order must be considered. For regular motions, the maximum error in forecasting the geosynchronous satellite position ranges from 0.14 to 2400 km, the error in forecasting the long semiaxis ranges from 0.013 to 1100 m, and the error in forecasting the subsatellite point longitude ranges from 0.069″ to 3.4° depending on the libration amplitude. The accuracy of forecasting depends on the libration amplitude: the less the libration amplitude, the higher the accuracy of forecasting. For quasi-random trajectories, the integration period for which the errors in forecasting do not exceed values obtained for libration motion is determined by the frequency and proximity of the trajectory to unstable stationary points. For the examples considered, this period is about 200 years. The estimated MEGNO factor confirms the efficiency of the numerical model of artificial satellite motion used to investigate the stochastic properties of geosynchronous satellite motion.     

The equation of motion for the trajectory of a circling particle with an overdamped circle center

Inspired by biological microorganisms swimming in circles in liquid with low Reynolds number, I developed the dynamic theory for computing the helical trajectory of a circling particle with an overdamped circle center. The equation of motion for the circling particle is a hybrid equation of deterministic terms and stochastic terms. Observing the motion of a swimming microorganism, I found the strength of stochastic fluctuations should be much smaller than that governs deterministic dynamics. This dynamic theory predicts a nonlinear transverse motion perpendicular to the direction of external force. Both the living microorganism and artificial circling particle are applicable for an experimental check of this prediction. For the convenience of easy theoretical research, I further derived the probability conservation equations based on this dynamic theory both in two-dimensional and three-dimensional space.     

快速反射镜在像移补偿中的应用

本文提出了一种基于快速反射镜的像移补偿方法用于解决航空成像中的像移问题。首先通过计算航空相机在曝光时间内的像移速度证明了像移补偿的必要性;针对快速反射镜存在伺服模型不确定性的问题,设计了模型参考自适应控制器;最后通过实验验证了该算法的性能,结果显示:采用本算法后,快速反射镜的阶跃响应稳定时间降低了50%以上,在振动情况下快速反射镜的稳定精度都可以达到10μrad,精度比传统控制方案提升10倍以上。最终的像移补偿成像实验成功验证了基于快速反射镜的像移补偿方案有较高的工程应用价值。     

Optimization and testing of the tomographic method of velocity measurement in the flow volume

The optic noncontact method of velocity field measurement in the flow volume is considered in this paper for the purposes of hydroaerodynamic experiment. The essence of this method is measurement of particles motion in the flow during short periods between laser pulses. This study offers and implements several algorithmic optimizations, allowing data processing time reduction. It is shown that application of threshold background filtering on the recorded projections (particle images) and fast estimation of initial intensity distribution in the volume allows increasing the speed of tomographic reconstruction algorithm two or three times. Reconstruction accuracy and errors in determination of particle shift were studied in this work using artificial images. The described tomographic method for the velocity field estimation in the flow volume was used for diagnostics of a turbulent submerged jet flowing into a narrow channel. The application of developed approaches in experiment allowed us to obtain spatial distribution of the average velocity field and instantaneous velocity fields in the measurement area.     

Compare study between smoothing efficiencies of epicyclic motion and orbital motion

The smoothing efficiencies of epicyclic motion and orbital motion in CCOS (computer controlled optical surfacing) were compared. CCOS polishing can smooth out mid-to-high spatial frequency errors which are smaller than tool size on optical mirrors due to the rigidity of polishing tools. The smoothing efficiencies of epicyclic motion and orbital motion with pitch lap and RC lap were compared and the result proved pitch lap with epicyclic motion smoothed ∼1.6 times faster than pitch lap with orbital motion while RC lap with epicyclic motion smoothed ∼1.85 times faster than RC lap with orbital motion.     

Barkhausen jumps in the motion of a single ferroelectric domain wall

It is shown that the motion of a domain wall in the improper ferroelectric-ferroelastic gadolinium molybdate Gd₂(MoO₄)₃ demonstrates a self-organized critical behavior under polarization reversal. Barkhausen pulses are measured experimentally during the jumpwise motion of a single plane domain wall in monocrystalline plates with artificial pinning centers of the “field inhomogeneity” type.     

Pinning effects on the vortex critical velocity in type-II superconducting thin films

We study the influence of artificial pinning centers on the vortex critical velocity in Al thin films deposited on top of a periodic array of Permalloy (FeNi) square rings. We demonstrate that the field dependence of the flux flow velocity strongly depends on the particular magnetic state of the rings. In particular, we find that, even when the rings are in a flux closure state, i.e. with little stray field, the vortex critical velocity shows a non-monotonic magnetic field dependence. This behaviour is in sharp contrast with the results obtained in a reference plain film, with no rings underneath. A comparison with the intrinsic strong pinning Nb films previously studied, suggests an interpretation in terms of a channel-like motion of vortices, here induced by the artificial pinning structure.     

On capillary motion of a viscoelastic liquid with a charged free surface

The structure of the capillary-relaxation motion spectrum in a liquid with a charged free surface has been investigated taking into account the viscosity relaxation effect. On the basis of numerical analysis of the dispersion equation for the wave motion in a viscoelastic incompressible liquid, it is shown that for a given wave number the range of characteristic relaxation times in which relaxation-type wave motion exists is limited and expands with increasing wave number. The growth rate of instability of the charged liquid surface markedly depends on the characteristic relaxation time and increases with its growth; in liquids with elastic properties, the energy dissipation rate of capillary motion is enhanced. At a surface charge density that is supercritical for the onset of Tonks-Frenkel instability, both purely gravitational waves and waves of a relaxational nature exist.     

Dynamics of individuals and swarms with shot noise induced by stochastic food supply

We study the Brownian dynamics of individual particles with energy depot in two dimensions and extend the model to swarms of such particles. We assume that the elements (energy depots) are provided at discrete times with packets of chemical energy which is subsequently converted into acceleration of motion. In contrast to the mechanical white noise which is incorporated in the equations of mechanical motion and has no preferred direction, the energetic noise, as discussed in this study, is directed and it does not reverse the direction of mechanical motion. We characterize the effective noise acting on the particles and show that the stochastic energy supply may be modeled as a shot-noise driven Ornstein-Uhlenbeck process in energy which finally results in fluctuations of the velocity. We study the energy and velocity distributions for different regimes and estimate the crossover time from ballistic to diffusion motion. Further we investigate the dynamics of swarms and find a transition from translational to rotational motion depending on the rate of the shot noise.     

人造地球卫星运动方程的代数动力学算法数值解

代数动力学算法首次被用于求人造地球卫星运动方程的数值解，在四阶算法下，与Runge-Kutta算法和辛算法的计算结果作了比较.结果表明，代数动力学算法对于人造地球卫星长期轨道的计算有较高的精度.并讨论了地球四极和八极带谐项对卫星轨道的影响. 关键词： 人造地球卫星运动方程 代数动力学算法数值解 地球四极和八极带谐项对卫星轨道的影响     

Motion by mean curvature by scaling a nonlocal equation: Convergence at all times in the two-dimensional case

The convergence to a motion by mean curvature by diffusively scaling a nonlocal evolution equation, describing the macroscopic behavior of a ferromagnetic spin system with Kac interaction and Glauber dynamics has recently been proved. The convergence is proven up to the times when the motion by curvature is regular. Here we show the convergence at all times in the two-dimensional case. Since, in this case, the only singularity is the shrinking to a point of a closed curve, we verify that the curve actually disappears past the singularity.     

高空核爆炸形成人工辐射带的数值模拟

基于Stmer关于带电粒子在地球磁场中运动的理论模型,分析得出高能电子在地球周围的运动区域.结合高空核爆形成放射性烟云的经验模型,推断高空核爆在地球周围形成人工辐射带的基本区域.进而利用高空核爆裂变特性和辐射带中高能粒子的分布特性,计算得到高空核爆形成人工辐射带的电子密度通量,并对高空核爆激发的人工辐射带特征与核爆炸的爆点纬度、高度及当量之间的关系作了初步的定量分析.数值模拟结果表明,在一定的条件下,0.1—1Mt TNT当量的高空核爆,预计在地球周围可形成电子通量密度比自然辐射带高3—4个量级的人工辐射带.形成的人工辐射带中心位置主要受核爆爆点地磁纬度的影响,核爆的爆高和核爆的当量则对人工辐射带的厚度及其中高能电子的通量密度有一定的影响. 关键词： 高空核爆 人工辐射带 高能电子通量 爆炸当量     

Recurrence Times in Quasi-Periodic Motion: Statistical Properties,Role of Cell Size,Parameter Dependence

We investigate the probabilistic properties of recurrence times for the simplest form of aperiodic deterministic dynamics, quasi-periodic motion. Previous results using number theory techniques predict two fundamental recurrence times for uniform quasi-periodic motion on a two-dimensional torus, while no analogous analytic result seems to exist for higher dimensional tori. The two-dimensional uniform case is reanalyzed from a more geometric point of view and new, workable expressions are derived that enable us fully to understand and predict the recurrence phenomenon and to analyze its parameter dependence. Emphasis is placed on the statistical properties and, in particular, on the variability of recurrence times around their mean, in relation to local Farey tree structure. Higher-dimensional tori are considered, and seen to also display a high variability in their finite-time recurrence behavior. The results are finally extended to the non-uniform quasi-periodic case.     

Dynamical derivation of momentum diffusion coefficients at collisions of relativistic charged particles

An expression has been obtained for the diffusion tensor of particles in the momentum space on the basis of the dynamics of particles motion. The general equations have been used to determine the rms momentum spread at collisions of relativistic charged particles at times shorter than the time of randomization of particles motion and at greater times when motion is completely random.     

In vivo anomalous diffusion and weak ergodicity breaking of lipid granules

Combining extensive single particle tracking microscopy data of endogenous lipid granules in living fission yeast cells with analytical results we show evidence for anomalous diffusion and weak ergodicity breaking. Namely we demonstrate that at short times the granules perform subdiffusion according to the laws of continuous time random walk theory. The associated violation of ergodicity leads to a characteristic turnover between two scaling regimes of the time averaged mean squared displacement. At longer times the granule motion is consistent with fractional Brownian motion.     

Self-propelled particles with soft-core interactions: patterns, stability, and collapse

Understanding collective properties of driven particle systems is significant for naturally occurring aggregates and because the knowledge gained can be used as building blocks for the design of artificial ones. We model self-propelling biological or artificial individuals interacting through pairwise attractive and repulsive forces. For the first time, we are able to predict stability and morphology of organization starting from the shape of the two-body interaction. We present a coherent theory, based on fundamental statistical mechanics, for all possible phases of collective motion.     

Quantum statistical effects of the motion of an oscillator interacting with a radiation field

The motion of a quantum oscillator interacting with a quantized radiation field is studied. The exact solution shows that the motion of the oscillator is described by a Langevin-type equation in which the friction and the effective frequency depend on time. The physical conditions under which these properties become constant are studied. The stochastic force becomes a gaussian process and in the limit of long times and weak coupling, has an autocorrelation function with the usual delta behavior.     

Induced magnetic monopole from trapped Λ-type atom

We investigate the spatial motion of the trapped atom with the electromagnetically induced transparency (EIT) configuration where the two Rabi transitions are coupled to two classical light fields respectively with the same detuning. When the internal degrees of freedom can be decoupled adiabatically from the spatial motion of the center of mass via the Born-Oppenheimer approximation, it is demonstrated that the lights of certain profile can provide the atom with an effective field of magnetic monopole, which is the so-called induced gauge field relevant to the Berry's phase. Such an artificial magnetic monopole structure manifests itself in the characterizing energy spectrum.     

成像光谱仪扫描镜运动准确度测量

扫描镜的运动准确度直接影响成像光谱仪对地运动补偿效果,为此研制了一套扫描镜运动准确度测试设备对其进行测量.首先分析了扫描镜的运动补偿原理,从理论上给出了运动补偿曲线;随后以15 m地面像元分辨率和系统调制传递函数下降2%作为依据分别确定了扫描镜的位置和速度准确度要求,列出了扫描镜运动补偿倍数与相对转速误差的关系.基于检定设备1/3法则提出了扫描镜运动准确度测试设备技术指标要求,接着以0.8″绝对式光电编码器为核心建立了一套扫描镜运动准确度测试装置,并从测试方法误差和编码器测角误差两方面对测试装置测角和测速准确度进行了详细分析;最后采用研制的测试装置对扫描镜的运动准确度进行了测量试验.试验结果表明扫描镜位置准确度优于3″±1.2″,4倍补偿时速度准确度为5.6%±1.29%,6倍补偿时速度准确度为3.85%±1.29%,满足成像光谱仪对扫描镜运动准确度要求.外场成像图像证明本文提出的扫描镜运动准确度测量方法及设备可用于成像光谱仪扫描镜的性能检测与验收.